Person: González Calbet, José María
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First Name
José María
Last Name
González Calbet
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
5 results
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Now showing 1 - 5 of 5
Item Interface double-exchange ferromagnetism in the Mn-Zn-O system: New class of biphase magnetism(Physical review letters, 2005) García, M. A..; Ruiz González, María Luisa; Quesada, A.; González Calbet, José María; Hernando Grande, AntonioIn this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn^(3+) and Mn^(4+) via a double-exchange mechanism. The presence of the ZnO around MnO_2 modifies the kinetics of MnO_2 →Mn_2O_3 reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.Item Temperature dependence of the magnetic properties in LaMnO_(3+δ)(Journal of applied physics, 2006) Romero, J.J.; Cuadrado, R.; Arroyo, A.; García, M. A.; Hernando Grande, Antonio; Cortés Gil, R; González Calbet, José María; Vallet Regí, María Dulce NombreData are presented on the thermal dependence of the hysteretic properties of cationic vacancies including manganite samples of composition LaMnO_(3+δ)(δ=0.05 and 0.12). Our results evidence the presence in both samples of two magnetic phases having ferro- and antiferromagnetic orders, respectively. The temperature dependence of the coercivity and relaxational properties of the samples is closely linked to the connectivity of the magnetic moment bearing Mn^(3+)-Mn^(4+) ferromagnetic clusters that demagnetize independently in the case of the δ=0.05 sample and collectively in that of the δ=0.12 one, as evidenced from the activation volume results (delta=0.05) which yielded a size of the same order magnitude as that obtained in previous works for the Mn^(3+)-Mn^(4+) ferromagnetic cluster size.Item Magnon-mediated magnetoresistance in layered manganites(Physical review B, 2019) Hernando Grande, Antonio; Cortés Gil, Raquel; González Merchante, Daniel; Hernando González, María; Alonso Rodríguez, José María; García García Tuñón, Miguel Ángel; Martínez, José L.; Ruiz Gonález, María Luisa; González Calbet, José MaríaWe describe here a type of magnetoresistance that takes place in naturally layered and outstanding ordered single phase manganites that may be mediated by magnon excitation. In particular, we show the effect for the Ruddlesden-Popper compound, LaSr2Mn2O7 synthesized by ceramic method. This material exhibits, besides the conventional colossal magnetoresistance, another type of magnetoresistance at low temperature, associated with breaking of the A-type antiferromagnetic coupling of Mn-containing planes. Excitation of magnons or application of a magnetic field breaks this antiparallel alignment so that some electrons, initially confined on the planes, become itinerant along the interplain directions through a double exchange mechanism, giving rise to resistance variations of the order of similar to 60% for polycrystalline samples. The effect described here might be present in other types of manganites exhibiting a natural layered structure, opening up the possibility of developing magnetoresistive devices based on antiferromagnetic oxide materials without requiring artificial multilayered structures.Item Magnetic field driving custom assembly in (FeCo) nanocrystals(Applied physics letters, 2006) Marín, P.; López, M.; Vlad, A.; Hernando Grande, Antonio; Ruiz González, María Luisa; González Calbet, José MaríaWe present the possibility of tuning the nanocrystalline microstructure of Co-rich samples by magnetic field annealing. Custom assembly of nucleated grains, aligned in the field direction, has been observed by means of high resolution transmission microscopy. The organized microstructure was obtained on the basis of the appropriate choice of composition, annealing temperature, related to the initial stages of nanocrystallization process, and magnetic field intensity. The linear pattern of the grains has been explained as a consequence of the counterbalance between magnetic, magnetostatic, and magnetocrystalline couplings, only relevant when the nucleation temperature is well below the Curie temperature of the nucleated phase.Item Ferromagnetism in fcc twinned 2.4 nm size Pd nanoparticles(Physical review letters, 2003) Sampedro, B.; Crespo del Arco, Patricia; Hernando Grande, Antonio; Litran, R.; Sánchez López, J. C.; López Cartes, C.; Fernández, A.; Ramírez, J.; González Calbet, José María; Vallet, M.The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.